The present invention relates to a super rigid rubber composition and a tire using the rubber composition, and more particularly relates to a super rigid rubber composition comprising a sulfur-vulcanizable rubber, N,N'-dithiodiamine or its derivative, a thermosetting resin and a curing agent, and a tire using the rubber composition as a tire part.
The inventors have made basic investigations for tire and found out that the use of a vulcanized rubber having a dynamic modulus of not less than 300 kg/cm.sup.2, preferably 500-1,500 kg/cm.sup.2, more preferably 700-1,500 kg/cm.sup.2, as a tire part, particularly as a bead filler rubber of a tire, improves remarkably the performance of the tire, and have further made various investigations in order to obtain a vulcanized rubber having such high modulus (hereinafter, such rubber is referred to as super rigid rubber).
In general, commonly used vulcanized rubbers have a dynamic modulus of about 20-100 kg/cm.sup.2, and the commercial production of vulcanized rubbers having a dynamic modulus of higher than about 100 kg/cm.sup.2 has various problems in the workability and processability. For example, a large amount of heat is generated due to the high rigidty of the rubber at the kneading in a Banbury mixer. Moreover, since a large amount of vulcanizer or vulcanization accelerator is used in order to increase the dynamic modulus of a rubber, the rubber scorches and an overload is subjected to the Banbury mixer. Further, when the rubber is extruded through a nozzle of an extruder, the nozzle is damaged due to the high rigidity and viscosity of the rubber or the rubber scorches, and the commerical production of the rubber is substantially impossible.